A continuously variable transmission whose available speed ratio range is expanded by employing a configuration of providing a sub transmission in series with respect to a variator (continuously variable transmission mechanism) and changing a gear position of this sub transmission mechanism according to a driving state of a vehicle without increasing a size of the variator is known.
JP5-79554A discloses a shift mode (hereinafter referred to as “synchronization shift”) which changes a speed ratio of the variator in a direction opposite to a speed ratio change direction of the sub transmission mechanism when changing a gear position of a sub transmission mechanism in such a continuously variable transmission equipped with the sub transmission mechanism. By performing this synchronization shift, speed changes of an engine and a torque converter decrease when the sub transmission mechanism is shifted, so that it is possible to reduce a shift shock due to these inertia torques.